Meters for metering the various forms of electrical energy are well known. Utility company meters can be of three general types, namely, electro-mechanical based meters (output generated by a rotating disk), purely electronic component based meters (output component generated without any rotating parts) and a hybrid mechanical/electronic meter. In the hybrid meter, a so-called electronic register is coupled, usually optically, to a rotating disk. Pulses generated by the rotating disk, for example by light reflected from a spot painted on the disk, are utilized to generate an electronic output signal.
It will be appreciated that the use of electronic components in electric energy meters has gained considerable acceptance due to their reliability and extended ambient temperature ranges of operation. Moreover, contemporary electronic signal processing devices, such as microprocessors, have a greater accuracy potential for calculating electrical energy use than prior mechanical devices. Consequently, various forms of electronic based meters have been proposed which are virtually free of any moving parts. Several meters have been proposed which include a microprocessor.
U.S. Pat. No. 4,298,839 - Johnston, incorporated herein by reference, discloses a programmable alternating current electric energy meter having a radiation responsive external data interface. The meter is shown to include a metering sequence logic control circuit which in the preferred embodiment is stated to be formed by a single-chip microcomputer, type MK 3870 available from Mostek Corporation of Carrollton, Tex. The logic control circuit is said to be operative to calculate and accumulate different measured parameters of an electrical energy quantity. Current and voltage components are provided to the logic control circuit from a convertor which produces current and voltage pulses at a rate proportional to the rate of the particular electrical energy consumed. The converter incorporates a rotating disk.
U.S. Pat. No. 4,467,434 - Hurley et al., discloses a solid-state watt-hour meter which includes a current sensing device and a voltage sensing device coupled to a Hall-effect sensing and multiplying device. The Hall-effect device is coupled to a microprocessor.
U.S. Pat. No. 4,692,874 - Mihara, discloses an electronic watt-hour meter which includes a single microprocessor and a power measuring device. The power measuring device is described as including an electric power converting circuit and a frequency divider. The electric power converting circuit provides an output pulse, the frequency of which is divided by the frequency divider. The frequency divider, however, is dependent upon a frequency dividing, ratio setting signal generated by the microprocessor.
U.S. Pat. No. 4,542,469 - Brandyberry et al., discloses a hybrid type meter having a programmable demand register with a two-way communication optical port. The demand register is said to include a central processing unit such as the NEC 7503 microcontroller. The microcontroller is utilized not only for controlling and monitoring the demand register, but also to perform power and energy calculations.
U.S. Pat. No. 4,884,021 - Hammond et al. discloses a meter for metering polyphase power sources wherein cycles for each phase are sampled at each degree and converted to a binary representation of amplitude. Conversion is described as being carried out in two steps, the first being a range conversion where the sampled amplitude is evaluated with respect to eleven possible ranges of amplitude or scaling factors. That range data is then stored and the sample is amplified in accordance with the desired range code and submitted to an analogue to digital converter. A general purpose digital signal processor is said to be utilized for treating the parameters derived from each sample and to develop pulse outputs which can be further processed or displayed by devices of conventional use in the industry. An electronic register is provided which is said to be controlled by a conventional microprocessor. The implementation of Hammond's range conversion scheme results in the energy measurement components effectively being "hard coded" with the particular metering scheme, thereby significantly reducing the adaptability of the meter for various known applications. The use of such a meter in the various utility company applications requires either keeping several different meter types in inventory, i.e. one meter type for each type of application, or one meter into which all application forms have been incorporated. It will be appreciated that one meter into which all application forms have been incorporated would be exorbitantly expensive.
Electronic meters such as those described above sense analog voltage and current signals and process digital representations of the voltage and current signals. Such meters provide electronic components including transistors, diodes, or analog-to-digital converter modules (ADCs) to convert the analog voltage and current signals into digital representations thereof. ADCs may be implemented according to a number of different techniques such as dual-slope integration, ramp-and-counter, successive approximation, and voltage-to-frequency conversion. However, none of these approaches have adequately provided the accuracy required by utilities for revenue metering while providing the dynamic range needed for wide voltage operating capability. Moreover, previous attempts to meet these requirements have resulted in complicated ADC circuits in which precise gain matching has been required.
Meters, such as those described above, which incorporate registers, are generally programmable at two levels. At the first level, firmware can be masked into a register in a relatively short period of time. At the second level, so-called soft switches can be programmed into non-volatile memory, i.e., electrically erasable programmable read only memory, to tell the firmware which algorithms to perform. Such systems work well for presently provided base metering data. However, such systems cannot change basic meter functions nor are they adaptable to use with additional hardware. While adequate for present applications, such metering systems are significantly non-flexible in relation to future needs and/or developments in both hardware and programmability.
U.S. Pat. No. 4,077,061 - Johnston et al. discloses a digital processing and calculating AC electric energy metering system. This system includes a single central processing unit for performing all energy determinations, system control and information display. Although this system does provide energy determination as output signals from the system, the system is not adaptable for modification of basic metering functions from external hardware or in relation to external communication signals.
Consequently, a need exits for an electronic meter which is designed to be programmable to the extent that basic metering functions can be changed relatively easily and which is economically adaptable for use with additional hardware. Such a meter would be capable of modification to handle various meter forms, to store calibration constants and to be capable of modification for future metering requirements. The present invention solves the aforementioned problems through the use of a distributed processing electronic meter incorporating a metering processor which is adaptable to multiple metering applications and which is utilized to perform all electrical energy determinations and a second processor which generates a display signal based on such electrical energy determinations, serves to control the overall operation of the meter and which provides access to processing, storage and display information for future hardware additions.